First, select the type of tree you want to decorate. If you have a real tree, make sure it is well watered and healthy. If you have an artificial tree, make sure it is set up and ready to go. Next, gather your ornaments. Choose a theme or color scheme that you like, and select ornaments that match. You can also add in other decorations such as garland, lights, and tinsel. Finally, begin hanging the ornaments on the tree, starting from the top and working your way down.